One kind of conventional heat sink currently used for heat dissipation in electronic components includes a plurality of radiation fins, and a base plate several times as large as the upper surface of the package of the electronic component (e.g., a CPU). Typically, the central portion of the base plate of the heat sink is made of a metal material having a larger thermal conductivity than the main material of the heat sink. However, there is a need for a heat sink having further enhanced heat dissipation capabilities for electronic components like the CPU of a personal computer or a large-scaled integrated circuit in order to cope with the trend of increasing heat generation of such electronic components due to the requirement for an even higher processing speed of a personal computer or a much more compact size of a IC component. For example, the increasing of the clock frequency and the number of gates will surely increase the heat generations of the electronic components.
An improved method for manufacturing the above-mentioned heat sink to enhance the heat dissipation was proposed by Kataoka (U.S. Pat. No. 6,367,152 B1).
In Kataoka's method, a metal material with larger thermal conductivity is joining integrally with the main material of the heat sink as a workpiece, and then forging the workpiece into a heat sink without the drawbacks of either the loss in heat transfer caused by the deformation of the metal plate or the deformation of the radiation fins caused by pretreatment when joining the metal plate to the base plate of the heat sink by screwing or brazing respectively. Kataoka's method includes the following steps: 1. nickel or tin plating on one surface or both surfaces of the two raw materials (for example: copper and aluminum); 2. brazing or soldering to join the two raw materials together into a workpiece; 3. putting the workpiece into the die; 4. forging the workpiece under the pressure to form a heat sink.
Please refer to FIGS. 1(a), 1(b), 2(a), and 2(b). FIGS. 1(a) and 1(b) are schematic diagrams showing a main material 1 and a heat transfer promoting material 2 with a higher thermal conductivity than the main material 1. As shown, the main material 1 and heat transfer promoting material 2 are joined integrally through nickel or tin plating and brazing to form a prior art workpiece 10. FIGS. 2(a) and 2(b) are schematic diagrams showing the workpiece 10 forged in a die 3 under pressure to form a semi-product of the prior art heat sink 4.
A problem with the prior art method is that, during the nickel plating process, heavy metal is released that can cause serious water pollution, or if tin plating is used, lead or zinc particles contained in the plating material are released into the air, which is harmful to the health of the workers during soldering process or anyone who is in the working area. Accordingly, the prior art method is a source of pollution and surely will cause the environmental protection concerns. Besides, the temperature of brazing is around 400° C., and there will be heavy metal particles contained in the brazing material that are released into the air, which is also harmful to the health of the workers of the brazing process or anyone who is in the working area. This is an even more hazardous source of environmental pollution. There are still other drawbacks like the high temperature of brazing will hurt the anodized surface formed during the plating process so as to hamper the quality of brazing, and will reduce the metal stress of the heat sink which will cause bending of the radiation fins while assembling with other parts (e.g., mounting on an IC package).
With the drawbacks of the prior art (discussed above) in mind, the applicant employed experiments and research full-heartily and persistently in an attempt to conceive an environmental protection concerned method for manufacturing heat sinks. The proposed method will not only solve the lead, zinc and heavy metal pollution problems but also decrease the manufacturing costs and improving the quality of the heat sinks.